Ingredients of cosmos

[dmg]

I read that dark matter accounts for 23% of the mass-energy content of the observable universe, while the ordinary matter accounts for only 4.6%. My question is which category do black holes fall into? Do you count them as ordinary matter?

 

If a massive star collapses, we get a black hole. What if a huge collection of dark matter collapses? Will we get a black hole again? I guess yes. Can we distinguish such two black holes? Can we count the latter black hole as part of dark matter?

[pantheory]

I read that dark matter accounts for 23% of the mass-energy content of the observable universe, while the ordinary matter accounts for only 4.6%. My question is which category do black holes fall into? Do you count them as ordinary matter?

 

If a massive star collapses, we get a black hole. What if a huge collection of dark matter collapses? Will we get a black hole again? I guess yes. Can we distinguish such two black holes? Can we count the latter black hole as part of dark matter?

I wouldn't be too enamored with percentages of dark matter or dark energy in the universe. Both are still considered by many to be only hypothetical. Black holes are presently not considered either matter or dark matter. So when they are proposing to sum up matter and dark matter in proportions, black holes are not considered in the equation.

 

There have been some black hole models that have proposed that their insides are a very dense form of matter such as a quark star, etc. There have been one or more other models that have proposed that black holes are a compressed form of dark matter, and still other(s) that propose that there is just one most fundamental particle that makes up everything.

 

If one looks at the prevailing dark matter models, most do not believe that if it exists that it could collapse becoming a black hole. The proportion of mass equivalence in black holes in the universe can be roughly calculated from the mass of the Milky Way without hypothetical dark matter, roughly 200 billion solar masses, and the mass of its central black hole of about 4 million solar masses. This is a ratio of about one fifty millionth of our galaxy which might be an extrapolated estimate of the universe as a whole.

 

So if this is a valid estimate black holes don't represent a very big portion of the universe in mass, very roughly one fifty millionth.

//

Edited May 28, 2012 by pantheory

[dmg]

pantheory, thank you for your reply.

[the asinine cretin]

dmg,

 

What an interesting question. I have no insight on the matter, but I'll definitely be following this thread. Good stuff.

 

Peace.

[swansont]

If a massive star collapses, we get a black hole. What if a huge collection of dark matter collapses?

 

Not clear to me how this would happen on a reasonable time scale. Normal matter forming stars and then collapsing is based upon all four of the basic interactions. If dark matter interacts only gravitationally, the only avenue for it to coalesce is for it to emit gravitational radiation.

[dmg]

If dark matter interacts only gravitationally, the only avenue for it to coalesce is for it to emit gravitational radiation.

 

Maybe I shouldn't have used the word 'collapse' for dark matter. If dark matter interacts only gravitationally, it probably much faster can form black holes.

[swansont]

Maybe I shouldn't have used the word 'collapse' for dark matter. If dark matter interacts only gravitationally, it probably much faster can form black holes.

 

No, I disagree, for the reasons I gave. Gravity is (almost) without dissipation. You'd never get a large mass density.

[dmg]

No, I disagree, for the reasons I gave. Gravity is (almost) without dissipation. You'd never get a large mass density.

 

Swansont, thank you for your replies.

 

Could you explain to me in more detail why gravitational energy has to be dissipated? Does it have anything to do with conservation of energy? It just cannot be locked up inside an event horizon and has to be dissipated?

 

 

 

What an interesting question. I have no insight on the matter, but I'll definitely be following this thread. Good stuff.

 

The asinine cretin, thanks.

[swansont]

Swansont, thank you for your replies.

 

Could you explain to me in more detail why gravitational energy has to be dissipated? Does it have anything to do with conservation of energy? It just cannot be locked up inside an event horizon and has to be dissipated?

 

If the energy is not dissipated the matter will not clump together. The potential energy turns into kinetic energy and vice-cersa, but that's the only option you have. To form a large mass density you'd need both low kinetic energy and low potential energy. You can't get to that without dissipation — you need a mechanism to shed the excess energy.

[pantheory]

dmg,

 

....explain to me in more detail why gravitational energy has to be dissipated? Does it have anything to do with conservation of energy? It just cannot be locked up inside an event horizon and has to be dissipated?

There are several ways energy can be converted concerning a pre-stellar nebula. One of the beginning ways that the energy of gravitational contraction is converted begins with the energy conversion into a gravitational vortex. Following that energy is absorbed by the friction of the vortex that turns into heat. Following that matter agglomerates at the center of the vortex and the energy of relative motion is converted into the energy of stellar compression. As the heat builds up it is radiated away from the vortex center.

 

In black hole theory the energy of influx accordingly turns into a torus and then into heat and accelerating momentum. If there is a great deal of matter in the torus then accordingly jets can form and much of the energy converted into these jets. Inside the event horizon energy could then be turned into the rotational momentum of the black hole. The in-falling mass will also be converted into the increased mass equivalence of the black hole. There is also theoretical Hawking radiation and outward moving theoretical waves called gravitational waves accordingly produced from the in-falling energy of matter.

//

Edited May 30, 2012 by pantheory

[Airbrush]

I read that dark matter accounts for 23% of the mass-energy content of the observable universe, while the ordinary matter accounts for only 4.6%. My question is which category do black holes fall into? Do you count them as ordinary matter?[/size][/font]

 

Black holes are considered baryonic dark matter, along with neutron stars, white dwarfs, and brown dwarfs, by Wiki. Planets and asteroids would be considered baryonic dark matter, if they cannot be detected. I suppose as soon as we can detect an exoplanet, it is no longer dark matter. They think most dark matter is non-baryonic.

 

 

"Early theories of dark matter concentrated on hidden heavy normal objects, such as black holes, neutron stars, faint old white dwarfs, brown dwarfs, as the possible candidates for dark matter, collectively known as MACHOs. Astronomical surveys failed to find enough of these hidden MACHOs. Some hard-to-detect baryonic matter, such as MACHOs and some forms of gas, were additionally speculated to make a contribution to the overall dark matter content, but evidence indicated such would constitute only a small portion."

 

http://en.wikipedia.org/wiki/Dark_matter

Edited May 30, 2012 by Airbrush

[dmg]

Swansot, Pantheory, Airbrush, thanks for your replies!

 

I read about hypothetical particles - weakly interacting massive particles (WIMPs) as possible solution to the dark matter. I wonder if these hypothetical particles obey the Pauli exclusion principle, or can they form a Bose-Einstein condensate?

 

 

[pantheory]

Swansot, Pantheory, Airbrush, thanks for your replies!

 

I read about hypothetical particles - weakly interacting massive particles (WIMPs) as possible solution to the dark matter. I wonder if these hypothetical particles obey the Pauli exclusion principle, or can they form a Bose-Einstein condensate?

Since dark matter is only hypothetical, the answer to your question would depend upon the reality of its existence. If you would assume that it exists then it would depend upon what particular model of dark matter particles that you are interested in. If dark matter was particulate and matter-like it would seemingly follow Pauli's exclusion principle like all other matter in general. Since dark matter, if it exists, would not be atomic matter it seemingly could not form a Bose-Einstein condensate.

//

Edited May 31, 2012 by pantheory

[dmg]

Thanks, pantheory.

 

 

 

[juanrga]

I read that dark matter accounts for 23% of the mass-energy content of the observable universe, while the ordinary matter accounts for only 4.6%. My question is which category do black holes fall into? Do you count them as ordinary matter?

 

Dark matter is a mere hypothesis. Black holes are not counted as dark matter.

 

If a massive star collapses, we get a black hole. What if a huge collection of dark matter collapses? Will we get a black hole again? I guess yes. Can we distinguish such two black holes? Can we count the latter black hole as part of dark matter?

 

Although GR predicts the formation of a black hole. The final result of a collapse is not clear when quantum gravity and other effects are considered. Several experts affirm that a black hole never form (and I recall that even Hawking is changing his mind about this).

 

The hypothetical concept of dark matter is not well-defined and there is no theoretical model that can predict what happens in a collapse

[pantheory]

juanrga,

 

....The final result of a collapse (of a stellar mass) is not clear when quantum gravity and other effects are considered.

(parenthesis added)

 

Quantum gravity is at best an alternative mainstream idea/ hypothesis. There is no presently acceptable working model of it.

 

Several experts affirm that a black hole never form (and I recall that even Hawking is changing his mind about this).

That black holes could never form, is contrary to mainstream theory. That stellar black holes can form by collapse of remnant stellar masses above the Chandrasekhar limit (~3 solar masses) following novas and supernovas, is presently well accepted theory. What a stellar black hole really is inside its very small diameter (as small as 15 miles) may be debatable since it depends upon the black hole theoretical model(s) that are being discussed.

//

Edited June 2, 2012 by pantheory

[dmg]

juanrga, thanks for joining in the topic.

 

I found an interesting discussion about dark matter on NPR http://www.npr.org/templates/story/story.php?storyId=6835217

 

There they say that in the past a crisscrossing network of strings of dark matter had formed a scaffolding upon which all ordinary matter later accumulated. Stars wouldn't have formed without this scaffolding. And we wouldn't have galaxies without dark matter.

[juanrga]

juanrga, thanks for joining in the topic.

 

I found an interesting discussion about dark matter on NPR http://www.npr.org/t...storyId=6835217

 

There they say that in the past a crisscrossing network of strings of dark matter had formed a scaffolding upon which all ordinary matter later accumulated. Stars wouldn't have formed without this scaffolding. And we wouldn't have galaxies without dark matter.

 

New observations are in contradiction with the dark matter model. Check for instance this recent ones

 

http://www.bbc.co.uk...onment-12571965

 

http://www.bbc.co.uk...onment-14948730

 

Any search of dark matter made in last decades has not found anything. I am convinced that dark matter does not exist.

 

Although GR predicts the formation of a black hole. The final result of a collapse is not clear when quantum gravity and other effects are considered. Several experts affirm that a black hole never form (and I recall that even Hawking is changing his mind about this).

 

That black holes could never form, is contrary to mainstream theory. That stellar black holes can form by collapse of remnant stellar masses above the Chandrasekhar limit (~3 solar masses) following novas and supernovas, is presently well accepted theory. What a stellar black hole really is inside its very small diameter (as small as 15 miles) may be debatable since it depends upon the black hole theoretical model(s) that are being discussed.//

 

As said above, if one considers only GR, a black hole with its corresponding horizon can form. The problem is that GR is very far from being a final theory... When one considers effects beyond the scope of GR, one obtains that a black hole never forms. As said above even Hawking is starting to change his mind and now he writes:

 

The way the information gets out [of a black hole] seems to be that a true event horizon never forms, said Hawking, just an apparent horizon.

 

Hawking lost the bet about black holes, because he was ignoring several technical details; although some of us warned him that his work was science fiction. When one adds additional corrections to the GR model, one finally finds that black holes never form.

Edited June 3, 2012 by juanrga

[pantheory]

As said above, if one considers only GR, a black hole with its corresponding horizon can form. The problem is that GR is very far from being a final theory... When one considers effects beyond the scope of GR, one obtains that a black hole never forms. ....................

The evidence that black holes exist is now beyond dispute. There is much dispute, however, regarding Einstein's model of them as vacuous points. There are many other theoretical models of them but none are presently considered to be any more valid. Mathematics aside, black hole models concerning something physical inside them, have a pretty big following and numerous proposals made. Here's just a few of the better known alternative models.

 

http://en.wikipedia....ack_hole_models

 

Hawking lost the bet about black holes, because he was ignoring several technical details; although some of us warned him that his work was science fiction. When one adds additional corrections to the GR model, one finally finds that black holes never form.

If GR is simply wrong, as some propose, then there could be no such thing as "adds additional corrections to the GR model." Because the mathematics of a model is functional in some venues does not mean that the underlying theory has validity, such as Newton's pulling force, Einstein's warped space, or Milgram's MOND, concerning a logical explanation of their formulations. None seemingly can answer questions like why matter has an associated pulling force, why is the universal gravity constant the value that it is, why should matter warp space, why the force of gravity changes at galactic scales, etc. Any logic so far proposed, if any, by these models seems to be unsatisfactory to those that think there is a simpler underlying logic explaining everything.

 

I think both dark matter and dark energy have reached the peak of their following and that dark matter is now on a downhill slide concerning the portion of astronomers and theorists that are strong advocates. In time I expect the same thing will happen to the dark energy idea, although I realize evidence for or against it will be even more difficult to come by.

//

Edited June 3, 2012 by pantheory

[juanrga]

The evidence that black holes exist is now beyond dispute. There is much dispute, however, regarding Einstein's model of them as vacuous points. There are many other theoretical models of them but none are presently considered to be any more valid. Mathematics aside, black hole models concerning something physical inside them, have a pretty big following and numerous proposals made. Here's just a few of the better known alternative models.

 

http://en.wikipedia....ack_hole_models

 

There are not evidence. The link that you cite is open to several objections. Who wrote the section "Alternative black hole models" seems to believe that a gravastar is another model of black hole, but the link to gravastars correctly emphasize that a gravastar is "an alternative to the black hole".

 

If GR is simply wrong, as some propose,

 

This has nothing to see with what I said.

Edited June 3, 2012 by juanrga

[pantheory]

There are not evidence. The link that you cite is open to several objections. Who wrote the section "Alternative black hole models" seems to believe that a gravastar is another model of black hole, but the link to gravastars correctly emphasize that a gravastar is "an alternative to the black hole".

My point is and was: there have been many mainstream models of black holes other than singularity models, and many alternative models to black holes such as gravistars.

 

(my quote)

If GR is simply wrong, as some propose

(your quote)

This has nothing to see (do) with what I said.

(parenthesis and deletion added)

Congrats on your English, I would wish that my Spanish would have so few errors as your English

 

(your quote)

When one adds additional corrections to the GR model, one finally finds that black holes never form.

Your quote asserts that GR with changes might disprove black hole theory. My quote was that if GR is wrong (concerning theoretical fundamentals) then changes to it will also probably be wrong, in my opinion.

//

Edited June 4, 2012 by pantheory

[juanrga]

 

(your quote) (parenthesis and deletion added)

Congrats on your English, I would wish that my Spanish would have so few errors as your English

 

Thank you for the correction!

[dmg]

New observations are in contradiction with the dark matter model. Check for instance this recent ones

 

http://www.bbc.co.uk...onment-12571965

 

http://www.bbc.co.uk...onment-14948730

 

Any search of dark matter made in last decades has not found anything. I am convinced that dark matter does not exist.

 

juanrga, I have read these BBC articles.

 

1) I don't see that the first one disproves dark matter. They say that Mond theory better predicts the relationship between gassy galaxies' rotation speeds and masses. However, the author conceded that "when you get up to the big scale of clusters of galaxies and you try to apply Mond to the whole thing, you fall short of fixing the missing mass problem".

 

2) In the second article they don't disprove dark matter either, they only suggest that instead of "cold" dark matter that formed within the first one millionth of a second after the Big Bang, the Universe may instead be filled with warm dark matter (WDM).

Where do you see a contradiction?

[juanrga]

juanrga, I have read these BBC articles.

 

1) I don't see that the first one disproves dark matter. They say that Mond theory better predicts the relationship between gassy galaxies' rotation speeds and masses. However, the author conceded that "when you get up to the big scale of clusters of galaxies and you try to apply Mond to the whole thing, you fall short of fixing the missing mass problem".

 

2) In the second article they don't disprove dark matter either, they only suggest that instead of "cold" dark matter that formed within the first one millionth of a second after the Big Bang, the Universe may instead be filled with warm dark matter (WDM).

Where do you see a contradiction?

 

I believed that titles/headings such as "Dark matter theory challenged by gassy galaxies result" would be self-explicative.

 

Some parts of the body of the news are not accurate and do no reflect what the studies show. For instance, it is misleading to say that MOND predicted the relationship better than dark matter, because the dark matter model makes no predictions and because the dark matter model cannot fit the data. From the PRL paper:

 

The specific BTFR that the data follow is unique to MOND. Indeed, to the best of my knowledge, MOND is the only theory to make a strong a priori prediction for the BTFR. The dark matter paradigm makes no comparably iron-clad prediction.

 

The expectation in LCDM is [...] This nominal expectation has the wrong slope and the wrong normalization.

 

The author, in the quote that you reproduce, is not suggesting that dark matter works for clusters. He is really saying that there exist observational uncertainties regarding clusters. He says in the paper:

 

While the bullet cluster is frequently cited as evidence against MOND, it is also problematic for LCDM. [...] Taken at face value, the bullet cluster would seem to simultaneously support and falsify both theories with equal vigor.

 

The second link reports additional difficulties with the dark matter model. The second link quotes to Frenck stating his belief that CDM would be substituted by WDM to avoid the difficulties reported. The problem is that WDM presents other difficulties over the CDM. For instance, the observed abundance of dwarf galaxies cannot be explained within LWDM models.

Edited June 6, 2012 by juanrga

[dmg]

In LCDM model http://en.wikipedia....ambda-CDM_model

 

There is dark matter density Omega_c and physical dark matter density Omega_c*h², where h is the reduced Hubble constant, h=100*H₀.

 

What is the interpretation of the dark matter density and the physical dark matter density?

What is it that is counted in one, but not in the other?